The present invention relates generally to array radiators, and more particularly the invention pertains to a means for increasing the power and field strength radiated by a solid state switched array radiator such as those used in ultrawideband radar systems.
Some array radiators use a pulsed transmission line that should be designed to preserve very fast rising pulses produced in each of a number of such pulsed lines that are triggered simultaneously or with appropriate delay to provide at the output of the pulse lines a voltage that is applied to antenna radiating elements.
The pulse lines can be stacked to have the effect of multiplying the voltage that is switched by a single Blumlein by approximately the number of Blumleins in the stack. The output end of the stack of Blumleins is arranged so that the voltages add to provide approximately N-times the voltage of a single Blumlein where "N" is the number of Blumleins. The Blumleins in the stack can either be triggered simultaneously by a single switching element, or by separate switches attached to each of the Blumleins that are triggered simultaneously. The Blumleins can be triggered either simultaneously or with an appropriate delay by having separate switches attached to each of the Blumleins that are triggered by laser diodes or other light sources that are themselves triggered simultaneously or with an appropriate delay. The ability to trigger with an appropriate delay allows one to tailor the arrival time of the pulses from each of the Blumleins in the stack to compensate for differences in geometry or to apply waveform shaping to the resultant freefield burst.
A limitation on the power radiated by solid state switched array transmitters is that the voltage that can be switched by reliable solid state switches (those that have greater than 10.sup.6 shot lifetimes) is currently about 80 kV and generally the switch lifetime tends to diminish as the voltage is increased. In fact, the current technology in manufactured solid state switched phased array transmitters is limited to switching at about 13 kV.
Blumlein pulser technology is mentioned in U.S. Pat. No. 4,335,462, the disclosure of which is incorporated herein by reference. This patent deals with an apparatus and method for generating a globe discharge with an application for pumping lasers. U.S. Pat. No. 5,044,004 describes a flash x-ray apparatus that uses Blumleins commuted by a single thyratron switch to change the output voltage and spectrum. In neither case do these patents apply an enhanced voltage to an ultrawideband antenna, nor do they provide a means for tailoring the waveform of an ultrawideband system. Moreover, in neither case are the Blumleins independently triggered.
The present state of the art in these transmitters involves using a single switching element for each radiating antenna and therefore the voltage applied to each radiating antenna is limited to 13 kV. This in turn requires a large number of radiating elements in order to high field strengths radiated from such arrays. It also, in cases where a small source is necessary, such as in ultrawideband radars, limits the field strength that can be radiated to modest levels. The incorporation of this invention into ultrawideband transmitters would usefully increase the field strength available from compact sources and would reduce the size of the array needed to produce very high field strengths at substantial ranges.